Safety regulations dictate, in the event of an impact such as a motor vehicle collision, that the amount of force/energy transmitted to the vehicle occupant's body cannot exceed a predetermined level in order to minimize the risk and/or severity of injury to the occupant. One way this is accomplished is to provide specific crumple zones in vehicle modules/panels, which absorb a portion of the energy of impact. Another way is to provide specific impact loading specifications, i.e., areas and structural features of the motor vehicle which are designed to fail at a predetermined impact load in order to mitigate and reduce the level of impact force transmitted to the occupant. In particular, it is known to provide brackets designed to fail at a predetermined impact load to accomplish this goal.
However, motor vehicle brackets and fasteners must meet certain durability/assembly requirements. For example, brackets and fasteners must be designed not to fail below preset limits, and also are often required to include design features which assist in alignment of the particular vehicle components which they secure. As an example, with reference to FIGS. 1A and 1B, conventional molded or cast bracket structures 10 for securing vehicle components (generically depicted as C, C′) one to another typically include a fastener locator portion 12 designed to auto-locate a fastener F such as a bolt or screw in a desired orientation for securing the bracket to a vehicle component. Conventional brackets 10 also typically include a solid body 14 which may optionally include one or more strengthening rib structures 16 to provide further stability and strength to the bracket. As depicted, bracket 10 is integral to the structure of vehicle component C, but the skilled artisan will readily appreciate that the bracket 10 may equally be a separately cast or molded piece. Because the bracket 10 presents a unitary body aligning the fastener locator portion 12 with a cooperating aperture 18 in a cooperating bracket structure 19 on an adjoining component C′, vehicle components C, C′ are rigidly secured to one another and there is no mitigation of impact force unless the bracket 10 completely fails and/or one or both of components C, C′ crumple or crush in the event of a collision.
With reference to FIG. 1C, another prior art bracket 10′ is shown which is designed to provide some impact force mitigation. The bracket 10′ includes a fastener F locator portion 12′ and a slip plane portion 18. In the depicted bracket, a two-way fastener locator portion 15 is provided by an arcuate top bracket edge. Arms 16′, 16′ depend from the top edge. The space 19 between the top edge and component C is substantially open. As will be appreciated, in the event of a direct or indirectly transmitted impact to component C, an impact load will be transmitted in the direction of fastener F (see arrow). As will be appreciated, this causes bracket 10′ and fastener F to function as a slip joint providing a certain degree of slippage on impact. The impact load at which the attachment between fastener F and the top edge will slip through space 19 is determined by fastener F clamping force. It is therefore very difficult to provide a precisely controlled slip plane which will slip only at a desired impact load. Moreover, over time and with the vibration encountered during vehicle use, fastener F may loosen resulting in noise, component vibration, etc.
Other bracket design options which are designed to reduce the impact forces transmitted by vehicle components/modules to lessen/mitigate risk and/or severity of injury can result in poorly secured or misaligned vehicle components, poor tactile “feel” of the vehicle to the vehicle user, noise issues such as squeaking/rattling, excessive vibration, etc. This can create customer dissatisfaction with vehicle quality, fit, and finish. On the other hand, brackets/fasteners which strengthen such areas may cause impact forces to a vehicle occupant to exceed desired levels. Thus, designing brackets and other attachments which are sufficiently durable, which provide other desirable features such as fastener location, but which are also designed to fail at a predetermined impact load presents a significant engineering challenge.
To satisfy this identified need in the art, the present disclosure describes a bracket for securing vehicle components/modules one to another. The described bracket includes suitable fastener locator structures, provides a durable structure providing a secure attachment of components during ordinary use, but is also designed to slip at a predetermined impact load in order to reduce the impact forces transmitted in the event of a collision. Advantageously, the bracket includes a slip plane portion providing a slip joint feature designed to cause joint or connection point slippage at a predetermined impact load. This slip joint feature is advantageous, in that the bracket on receiving a predetermined impact will slip rather than completely failing, providing an impact absorbing function without completely releasing the connection between the components. The described bracket further includes a “tunable” portion which allows the designer to increase or decrease the predetermined impact load which will cause the bracket to slip.